Modular steel concrete reinforcement system

ABSTRACT

A method of welding reinforcement steel bars (rebar) and assembly of fusion-welded rebar into panel assemblies that are self-stabilizing to withstand the rigors of transport to and positioning within construction sites. The rebar welding method generates fusion welds in such a manner that the weld imparts stability and strength to the welded rebar assemblies. The rebar welds permit the assembling of larger and more varied rebar panel configurations without the need for tie wire or other coupling devices. Further, the welded panels allow positioning of large rebar configurations, insuring that the spacing of the individual bars exceeds all required tolerances. The self-stabilizing fusion rebar welding process allows a more efficient, flexible and rapid method of rebar panel construction by using assembly systems on mobilized trailers or at stationary locations.

PRIORITY CLAIM

[0001] This application claims priority to U.S. Provisional ApplicationSer. No. 60/193,408, entitled Modular Steel Concrete ReinforcementSystem, filed Mar. 29, 2000.

FIELD OF THE INVENTION

[0002] This invention relates generally to concrete reinforcing steelconstruction and, more specifically, to the efficient prefabrication andnon-structural welding of rebar panels for use in concrete structures.This invention further relates to the fabrication of welded rebar panelson site as well as off site, thereby reducing the cost associated withtime, material and labor.

BACKGROUND OF THE INVENTION

[0003] Currently, rebar panels are constructed by wire tying, mechanicalcouplers, and occasionally by a combination of welding and wire tying.All of these processes are costly because they are labor intensive andtime consuming. Further, inherent weaknesses within each method limitsthe size and shape of panel that can be produced, thereby increasing thesteps and thus costs in the overall construction process. As a result,conventional reinforcement steel bars (rebar) assembly methods requiremore steps with increased costs, resulting in the construction ofstructurally compromised rebar panels.

[0004] Tie wire constructed rebar panels often structurally fail forseveral reasons. Firstly, the connection resulting from the tyingprocess is subject to human inconsistencies. For example, the tie wireconnection is only as strong as the individual person making the tie.Thus, structural inconsistencies often exist in panels where more thanone person is constructing a panel, or a single person becomes fatiguedwhile doing so.

[0005] Even if tied correctly, tied rebar connections severely limitpanel size due to wire strength and overall rebar intersection rigidity.Typically, the panels are assembled and tied with the assembly laid outon the ground near the job site. Upon completion of the tying process, acrane or other machine is used to place the panel in the concrete form.Wire tied panels are often incapable of supporting the panel's weightduring their placement, often yielding a displacement of the tied rebarmembers known as “raking.” As the spacing of the rebar must be madewithin the tolerances specified by the engineer, the displaced rebarmust be retied in its specified location increasing labor costs.

[0006] Not too different from the tied rebar panels are panelsconstructed with mechanical rebar couplers. Here, a great variety ofmechanical couplers are applied to intersections of the rebar panel inplace of wire ties. The couplers are more time consuming to use than thewire tie method discussed above. Generally, however, a more consistentrebar connection is attained when using the mechanical coupler over thetie wire panel construction technique. Thus, when the mechanicalcoupling is done properly a more consistent panel construction isachieved. However, panels constructed with mechanical couplers are verycostly with regards to the multiple steps required to assemble them andthe price of the couplers themselves.

[0007] Finally, attempts have been made to produce a welded rebar panel.Historically, these attempts have yielded a sub-standard product. Allprior welding techniques have not achieved metallurgical propertiesmeeting the requirements for reinforced concrete. Rebar in concrete isdesigned to support tensile loads; therefore, welds must not compromisethe ability of the steel to support such loading. Consequently, a rebarpanel constructed with welds not having appropriate metallurgicalproperties is not desirable and may increase the likelihood of astructural failure.

[0008] The present invention is directed to a system and method for theconstruction of weld-stabilized rebar panels that overcomes theabove-mentioned problems.

SUMMARY OF THE INVENTION

[0009] The present invention comprises a system for the construction ofweld-stabilized rebar panels using a plurality of spot fusion welds madeby a unique gas metal arc welding (GMAW) process. The system and methodincludes rapidly welding rebar sections using GMAW to obtain a fusionweld joint. The system includes a rebar shear used to cut the rebar topredetermined lengths, a rebar bender used to impart required curvatureto the rebar, a welding jig used to align the rebar in the desired rebarpanel configuration, a rebar welder, preferably a gas metal arc welder,a power source, and one or more rolling tables facilitating the movementof the rebar from the rebar shear to the rebar bender and ultimately tothe welding jig. In operation, the rebar starts at the rebar shear,where the rebar is cut, as necessary, to predetermined lengths. Therebar then travels along the rolling tables to rebar bender, where anyrequired curvature is imparted to the rebar. The rebar is then forwardedalong rolling table to the welding jig, where is comes to a stop alignedwithin the jig to facilitate intersection with other rebar in the panelassembly. Once the rebar is properly aligned in the welding jig, therebar welder, powered by the power source, is used to fusion weld therebar intersections.

[0010] Specific settings are used on the welder and the power source inorder to achieve a flare bevel groove weld that meets the grade A706requirements. The use of shielding gas in the method contains not onlyheat, but also helps create the fusion between the rebar and consumableelectrode of the welder without causing any carbon breakdown in theheat-affected zone of the rebar, thus maintaining the rebar ductilityand the specific advantages of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The preferred and alternative embodiments of the presentinvention are described in detail below with reference to the followingdrawings.

[0012]FIG. 1 is a depiction of a welded rebar panel manufacturing centermade in accordance with the present invention;

[0013]FIG. 2 is a top view of a welding jig made in accordance with thepresent invention;

[0014]FIG. 3 is a side view of a welding jig of the present invention;

[0015]FIG. 4 is a depiction of a portable welded rebar panelmanufacturing center made in accordance with the present invention;

[0016]FIG. 5 is a top view of a stationary welded rebar panelmanufacturing center made in accordance with the present invention;

[0017]FIG. 6 is a side view of the building component of a stationarywelded rebar panel manufacturing center of the present invention;

[0018]FIG. 7 depicts an alternative embodiment of a welded rebar panelmanufacturing center of the present invention; and

[0019]FIG. 8 is a lifting device made in accordance with the presentinvention..

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0020] The present invention provides a system and method forconstruction of weld-stabilized rebar panels. By way of overview andwith reference to FIG. 1, the preferred embodiment of the presentinvention includes a welded rebar manufacturing center 10 including arebar shear 12 used to cut the rebar to predetermined lengths; a rebarbender 14 used to impart required curvature to the rebar; a welding jig16 used to align the rebar in the desired rebar panel configuration; arebar welder 18, preferably a gas metal arc welder (GMAW); a powersource 20, such as an 100-185 KW electrical generator (for example, aLincoln Power Source 400); and one or more rolling tables 22facilitating the movement of the rebar from the rebar shear to the rebarbender and ultimately to the welding jig. In operation, the rebar startsat rebar shear 12, where the rebar is cut, as necessary, topredetermined lengths. The rebar then travels along rolling table 22 ato rebar bender 14, where any required curvature is imparted to therebar. The rebar is then forwarded along rolling table 22 b to weldingjig 16, where is comes to a stop aligned within the jig to facilitateintersection with other rebar in the panel assembly. Once the rebar isproperly aligned in the welding jig, rebar welder 18, powered by powersource 20, is used to fusion weld the rebar intersections, and describedwith more particularity below.

[0021] Welding jig 16 is described in more detail with reference toFIGS. 2 and 3. Welding jig 16 includes a frame 30, a base referencespacer 32, an adjustable stop bar 34, and adjustable stopping pins 36for placing the rebar in the desired spatial relationship to theintersecting rebar. In the preferred operation of this embodiment, alayer of rebar is placed in jig 16 and is held in proper spatialrelation to the intersecting rebar via base reference spacer 32 andspacer bar 34. Subsequently, as the adjacent layer of rebar is applied,adjustable stop pins 36 dictate the proper spacing of the rebar.

[0022] Critical to the ability of the rebar to function as a tensionalload-bearing member is the maintenance of the rebar metallurgicalproperties. A specific welding process to achieve a flare bevel grooveweld of grade A706 must be carried out to ensure that the metallurgicalproperties of the rebar is not compromised during the fusion weld. Afterextensive experimentation, its was determined that this welding processis accomplished as follows.

[0023] In the preferred embodiment, specific settings are used on welder18 and power source 20 in order to achieve a flare bevel groove weldthat meets the grade A706 requirements. With respect to welder 18,initially the shielding gas supply hose of the welder (not shown) mustbe disconnected and a flow filter with manual adjustment attached. Thisresults in diffusing the typical narrow flow pattern to a more openspray pattern. The gas flow rate is set to approximately 35 cubic feetper hour. The spot time on the welder is set to approximately 0.02seconds, and the voltage to approximately 26 volts. A 0.046 inchdiameter or equivalent I. E. Murimatic D2-ER80s-D2 electrode wire is fedinto the welding area at a feed rate of 350 inches per minute.Additional adjustments are likewise made with respect to power supply20, preferably an electrical power generator. Specifically, the cover ofthe electrical generator is removed, after which the main feed cable isremoved from the internal breaker. Next, a voltage booster is insertedwhere the main feed cable was previously attached. Following theinsertion of a voltage booster, the main feed cable is attached to thevoltage booster in a manner understood by those skilled in the relevantart, or as specifically indicated on the junction plate of a LincolnPower Source 400. In the preferred embodiment, and as applied using anelectrical generator, the selected arrangement is Red=Black, 0=Green,B=White. In this manner, the required voltage (optimally 25-volts) isachieved at an even ratio in order to create the desired weld withoutaffecting the metallurgical properties of the rebar.

[0024] In operation of the GMAW rebar welder upon rebar sections in thewelding jig, the weld area is flooded with an Argon-Carbon Dioxideshielding gas (approximately 90% Argon, 10% CO₂). The Argon/CO₂shielding gas pours at approximately 35 cubic feet per hour (CFH).Filler weld material grade LA90 or Murematic D2—single shield or dualshield consumable electrode—is placed near the rebar intersection areas.In a preferred embodiment, an arc is struck for two or three seconds,resulting in a molecular fusion weld approximately ¼ to ⅝ inches long.It will be appreciated that longer or shorter welds may also be made. ByAmerican Welding Society standard, a flare bevel groove weld isproduced. This welding process is repeated at all or a desired subset ofrebar intersections of a panel.

[0025] The shielding gas contains not only heat, but also helps createthe fusion between the rebar and consumable electrode without causingany carbon breakdown in the heat-affected zone of the rebar, thusmaintaining the rebar ductility. Based on experimentation, usingArgon/CO₂ shielding gas with the 90/10% ratio and at approximately 35CFH flow rate obtains the strongest fusion rebar weld. A rebar panelcontaining a plurality of such fusion welds is inherently strong andself-stabilizing. Thus, the fusion welded rebar panels do not requireany additional stabilizing structure to maintain panel integrity. Anindependent testing facility was employed to examine the strength valueof the weld and to examine the overall effect of the weld on thestructural integrity of the rebar. The conclusions reached byresearchers at the independent testing facility are presented inAppendix A and incorporated by reference herein.

[0026] The present invention anticipates a variety of alternativeembodiments of the welded rebar manufacturing center without deviatingfrom the scope of the present invention.

[0027]FIG. 4 discloses a portable welded rebar panel manufacturingcenter 40 made in accordance with the present invention. The portablewelded rebar panel manufacturing center is mounted on a movable vehicle,such as a trailer, but otherwise includes the same components asdescribed above, namely, rebar shear 12; rebar bender 14; welding jig16; rebar welder 18; power source 20; and one or more rolling tables 22.The portable manufacturing center is designed to be transported to aconstruction job site for manufacture of rebar panels of various sizes.This portable version of the invention is especially useful forproducing large welded rebar panels that are difficult to transportintact from remote manufacturing facilities using existing technology.In addition, the portable manufacturing center is useful when especiallycomplex panels are required in the construction process.

[0028] An alternative embodiment is shown with reference to FIGS. 5-7,which disclose a stationary welded rebar panel manufacturing center 50.FIG. 5 discloses a building 52. At an end of the building is a pile ofstock rebar 54—no precut rebar is necessary. Within the building is awelded rebar manufacturing center similar to system described above.Following the same processes disclosed above, welded rebar panels areproduced. The welded panels are then placed on a transport vehicle 56and hauled to the construction site. FIG. 6 discloses a frontal view ofthe stationary center in which a plurality of welded rebar manufacturingcenters 60 are employed. In this manner, the production capabilities ofthe stationary center is greatly improved. Further, a loading space 58is maintained between the assembly systems 50 to allow efficienttransport of the completed welded panels. The stationary center isgenerally more useful when employed with smaller welded panels moreeasily capable of being transported to the construction site from aremote location. FIG. 7 discloses the welded rebar panel manufacturingcenter having similar components but a slightly different layout inwhich additional rolling tables are added and the welder is locatedbetween the welding jig and the rolling tables.

[0029]FIG. 8 is a lifting device 70. The lifting device is used to movecompleted welded rebar panels from the welded rebar panel assemblycontrol, whether the portable or stationary, to transport vehicle 56, toa the concrete form (not shown), or to a storage pile (not shown). Inthe preferred embodiment, a cable is attached to a picking eye 72 of thelifting device. The picking eye is also connected to a spreader bar 74,which in turn attaches to evenly spaced cable connectors 76. The cableconnectors are attached to the welded rebar panel to facilitate movementof the panels to the desired location.

[0030] While the preferred embodiment of the invention has beenillustrated and described, as noted above, many changes can be madewithout departing from the spirit and scope of the invention.Accordingly, the scope of the invention is not limited by the disclosureof the preferred embodiment. Instead, the invention should be determinedentirely by reference to the claims that follow.

APPENDIX A Concrete Reinforcement Bar Spot Weld Evaluation

[0031] 1.0 INTRODUCTION

[0032] A unique spot welding process has been developed to be used whenappropriate in lieu of ties between reinforcement bars being placedprior to pouring concrete. This evaluation was completed to qualify theprocess based on testing and analyses. The rebar spot welds wereexamined for strength and ductility. Furthermore, the effect of thewelding on the reinforcement was examined to ensure the process does notdegrade the material strength or ductility.

[0033] 2.0 PLAN OF APPROACH

[0034] Specific issues of concern are the weld strength and ductility aswell as quantification of the effect of the weld on the reinforcement. Atest program was procedurized and testing completed to collectlaboratory data appropriate for analyses and evaluation of the weldprocess suitability. The following evaluation summary memorializes theprogram results.

[0035] 3.0 EVALUATION SUMMARY

[0036] The minimum failure load and rotational angle at failure are 120pounds and 19°. This failure load is compatible with the materialstrength. All failure surfaces show ductility.

[0037] The welding process does not degrade the reinforcement strength.The weld and HAZ are stronger than the parent material and did notexhibit any non-ductile behavior.

[0038] 4.0 TEST AND INSPECTION PROGRAM PROCEDURE

[0039] A total of eight specimens will be tested. Four of them shall bewelded #4 bars and four welded #8 bars. The specimens shall beidentified, photographed, and visually inspected prior to testing. Theinspection results shall be recorded. It is necessary to note the weldlocations and sizes as well as any weld defects such as undercut or lackof fusion.

[0040] Two twisting and two rolling bend tests shall be conducted foreach specimen size as shown in the following figure. The specimens shallbe rigidly restrained and loaded to failure. The maximal load applied aseach specimen is broken shall be recorded in the following load datasummary table along with the rotation angle at maximal load application.

[0041] The broken specimens shall be photographed and visuallyinspected. The inspection results shall be recorded. Pretest inspectioncorrelations comments must be made.

[0042] Specimen weld failure surfaces shall be photographed and thefailure surface characteristics shall be noted to establish whetherductile or brittle failures occurred. FAILURE LOAD TABULATION FailureLoad Rotational Angle at Specimen Test condition (Pounds) Failure(Degrees) 4-1 Twisting 4-2 Twisting 4-3 Rolling 4-4 Rolling 8-1 Rolling8-2 Twisting 8-3 Twisting 8-4 Rolling

[0043] One piece from each type of broken specimen shall be selected andsectioned through the broken weld so that microstructure andmicrohardness characteristics may be obtained in the weld, heat affectedzone, and parent material. The specimens (4) shall be appropriatelyetched and photographed to show the metallurgical characteristics of theweld, heat affected zone, and parent material. Microhardnesses shall berecorded in the following data summary table. This same size (4)provides confidence that the complete weld population (16) does notcontain different attributes.

[0044] The data required by this test program procedure shall beincluded as the following section of this evaluation. MICROHARDNESS DATASUMMARY Weld HAZ Material Specimen (HRC) (HRC) (HRC) 4-1 4-2 4-3 4-4 8-18-2 8-3 8-4

[0045] 5.0 TEST AND INSPECTION PROGRAM RESULTS

[0046] A Failure Load Tabulation and Microhardness Data Summary follow:FAILURE LOAD TABULATION Failure Load Rotational Angle at Specimen Testcondition (Pounds) Failure (Degrees) 4-1 Twisting 120 19 4-2 Twisting200 28 4-3 Rolling 280 27 4-4 Rolling 210 28 8-1 Rolling 320 50 8-2Twisting 615 36 8-3 Twisting 415 42 8-4 Rolling 505 35

[0047] MICROHARDNESS DATA SUMMARY Weld HAZ Material Specimen (HRC) (HRC)(HRC) 4-1 33.5 45.0 87.0 4-2 35.0 32.0 85.0 4-3 39.0 45.0 86.0 4-4 35.040.0 88.0 8-1 36.0 45.0 93.0 8-2 33.0 40.0 91.0 8-3 32.0 47.0 96.0 8-428.0 44.0 91.0

[0048] Test and inspection program results follow on aspecimen-by-specimen basis. Pretest specimen photographs and inspectioncomments are followed by equivalent posttest information. Maximal loadsand deflections are summarized. Lastly, failure surface and materialphotomacrographs are provided with a microhardness data recapitulation.

[0049] The minimum failure load and rotations angle at failure are 120pounds and 19°. All failure surfaces show ductility. The minimumultimate parent material strength converted from HRB data is 81 ksi. Theminimum HAZ and weld material ultimate strength converted from HRC dataare 150 ksi and 134 ksi respectively. The weld and HAZ are stronger thanthe parent material and they did not exhibit any observed non-ductilebehavior. Failure loads are compatible with the material strength.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
 1. A method of rapidly welding rebar sections using gas metal arc welding (GMAW) to obtain a fusion weld joint, comprising: shearing the rebar sections into lengths appropriate for a construction application; bending the sheared rebar into shapes appropriate for the construction application; placing the rebar sections into a welding jig; positioning the rebar sections to physically touch and intersect at a desired location; adjusting an electrical power source; positioning a welding rod at a rebar intersection point; positioning a filler material at the weld location; delivering a shielding gas to the weld location; applying electrical power to a welding electrode wire using an electrical power delivery system; and arcing said electrode wire at the intersection point to form a fusion weld joint.
 2. The method of claim 1, wherein the rebar is grade A706 steel.
 3. The method of claim 1, wherein the filler material is grade ER80S-D2.
 4. The method of claim 3, wherein the filler material comprises: grade LA90; and, grade Murematic D2.
 5. The method of claim 1, wherein the shielding gas comprises: about 90% argon; and, about 10% carbon dioxide.
 6. The method of claim 1, wherein the flow rate of the shielding gas is about 35 cubic feet per hour.
 7. The method of claim 1, wherein the power delivered by the welder comprises about 100 to 185 kilowatts.
 8. The method of claim 1, wherein the electrode wire comprises: a solid electrode wire of about 0.045 inches diameter single shield; and a flux core electrode wire of about 0.045 inches diameter single shield.
 9. The method of claim 8, wherein the electrode wire feed rate is about 350 inches per minute.
 10. The method of claim 1, wherein the electrical power is applied to the wire at about 0.02 seconds spot time.
 11. The method of claim 1, wherein the combined weld time is about 2 - 3 seconds.
 12. The method of claim 1, wherein the dimension of the fusion weld is about ¼ - ⅝ inches.
 13. The method of claim 1, wherein the fusion weld joint comprises: a butt joint; an overlap joint; and a cross joint.
 14. An system for producing GMAW fusion welded rebar panels using rebar, comprising: a rebar shear used to cut the rebar into lengths appropriate for a construction application; a rebar bender used to impart curvature to the rebar appropriate for a construction application; a welding jig used to align the rebar in the desired rebar panel configuration; at least one rolling table facilitating the movement of the rebar; a gas metal arc welding unit; and an electrical power generator delivery system capable of delivering electrical power to the gas metal arc welding unit.
 15. The system of claim 14, wherein the assembly system is stationary.
 16. The system of claim 14, wherein the assembly system is portable. 